Gold plating



Nov. 10, 1964 R. DuvA ETAL 3,156,634

GOLD PLATING Filed Deo. 12, 1962 24M/WM United States Patent O 3,156,634 GOLD PLATDIG Robert Duva, Paramus, and Donald Gardner Foulke,

Watchung, NJ., assignors to Sel-lex Corporation, Nutley, NJ., a corporation of New Jersey Filed Dee. 12, 1962, Ser. No. 244,204 9 Claims. (Cl. 20d-43) This invention relates to the deposition of gold and is especially related to the deposition of pure, 24-carat gold.

Pure gold is commonly plated from a potassium cyanide solution operated at about 60-70 C. and as is common with cyanide baths heavy deposits tend to become rough and lacking vin density from a structure standpoint. Furthermore, such solutions tend to decompose to yield cyanide breakdown products which are deleterious. Carbon treatment then is required and even continuous carbon treatment has proved to be inadequate for some of the recent rigid specification-s estab-lished. Among Ithe objects of the invention, therefore, is to provide an improved process and bath for depositing substantially pure gold electrolytieally.

Although the process and composition is especially related to the electrodeposition of pure gold, it has also been found advantageous in the deposition of alloy gold, l to 24 carat gold, for example, `and the bath can contain up to abou-t 18 g./l. of a base metal ion.

This application is a continuation-in-part of US. application Serial No. 106,924, led May l, 1961, now abandoned.

The acid gold solutions described by Rinker and Duva in Patent No. 3,104,212 provided a means whereby heavy, sound gold deposits could be obtained by depositing the `gold from a solution containing potassium gold cyanide and the salts ot weak organic acids at a pH of 3-6 from room temperature to about 70 C. Similarly mirror bright alloy gold deposits are obtained by the process and composition disclosed in US. 2,905,- 601.

The present invention is based on the discovery that 3,156,634 Patented Nov. 10, 1964 ice alkyl of 6 carbon atoms or less and an aryl group conand OH, where R1 is selected from the group consisting of hydrogen, an alkyl group of -up to 6 carbon atoms and an aryl group of up to 6 carbon atoms. It hydra- Zine or its related compounds, as defined, per se, are added to the bath, the salt :may be formed within the bat-h. In the claims, therefore, it will be understood ythat a bath which contains a salt of hydrazine or its related compounds (as defined) will be understood to contain hydrazine or the related compound.

FIGS. 1 and 2 are photornicrographs of a cross section of tba-sis metal with a gold plating thereon.

Where an alloy gold is to be deposiited the metal to be alloyed with the gold may be, for example, arsenic, cobalt, chromium, iron, tin, nickel, antimony, manganese, etc., and is added in a form of soluble salt or complex which provides the metal in the cathode lm in a form, probably ionic, such that it will codeposit the gold. With alloy gold a primary advantage of the addition is in reducing stress in the deposit.

The method or carrying out this invention will become clear in the examples to follow.

Example 1 posit was semi-bright and particularly uniform. The

deposits from such an acid solution can be ygreatly imr proved by the addition of small amounts of hydrazine and substituted hydrazines and salts of hydrazine and substituted hydrazine. The deposits become send-bright to almost bright, are extremely smooth and particularly receptive to soldering and gold alloy die attachment operations. Furthermore, the .pH range ot operation of the bath can be extended to from 2.5 to 7L0.

The exact mechanism of .the action of hydrazines in such a system is unknown, however, it is known that as gold is plated'ont of such solutions and additional gold is added in the form of potassium gold cyanidethe common commercial procedure-buildup of some KCN must occur. This Would naturally tendto cause the formation of the type of deposit obtained from cyanido formations, in a reduced amount torbe sure. Substituted hydrazines are known to react with cyanide in the presence of copper and other metal cyanides (Sand- Ineyer reaction) and it is possible that this explains the eiect; then again, it may be that isocyanates or isocyanides are for-ined.

In any event, there is a definite improvement inv deposits obtained from organic acid gold baths containing hydrazine and related compounds and the salts of hydrazine and related compounds conforming to the structure,

Where R is selected from the group of hydrogen, an

photomicrograph attached indicates an exceedingly sound eposit. ee FIG. 1.

Example 2 To a bath as described in Example 1, absent the hydrazine sulfate, was added'S g./l. of methyl hydrazine. Excellent deposits were obtained, see FIGURE 2, at 0.2

Example 3 1,1-dimethylY hydrazine, 5 g./l., was substituted for the methyl hydrazine of Example 2. Again, excellent, sound, semi-bright deposits Were obtained at 0.2 amp/ din?.

Example 4 A bath was made up containing 50 g./l. of citric acid, g./l. of potassium citrate and 8 g./l. of gold as potassium gold cyanide. The pH was 4.2. To this standard bath was added 5 g./l. of hydroxyl amine hydrochloride. At 60 C. and 0.2 amp/dm.2 a yellow, .sounddeposit was obtained, 3.068 g. depositing in 4 hours at 0.2 amp/dm?.

Example 5 Exmzple 6 To the standard bath as disclosed in Example 3 was added 10 g./l. of urea. The deposit obtained was sound and the efficiency was 120 ing/ampere minute.

In other experiments the same characteristic linegrained deposits were obtained over wide current density ranges, 0.1-1.5 ampcres/drn.2 with 4 to 16 g./l. or" gold, and lO-ZOO g./l, of an organic acid ion, usually citric acid. The pH was not as critical as when :the bath was operated without the hydrazine type additions and the bath could be operated at pH values from 2.5 to 7.0.

Example 7 A bath Was made up containing 50 g./l. of potassium citrate, 10 g./l. of citric acid and 8 g. of gold as potassium gold cyanide. The pH adjusted to 4.2. To the bath was added 6 g./l. of hydrazine sulfate and 60 g./l. of nickel as nickel citrate. Excellent stress-free deposits were obtained to a thickness of 20 microns at 1.0 a./dm.2. Without the hydrazine sulfate stress was much greater.

Example 8 The process was conducted as in Example 7 but 0.06 g./l. of arsenic added as arsenic citrate was substituted `for the nickel. The bath was operated at a current density of 1.0 a./drn.2 and excellent stress-free deposits were obtained.

Example 9 The process was conducted as in Example 7 except that 0.5 g./l. of cobalt added as cobalt sulfate was substituted for the nickel of Example 7. The bath was operated at a current density of -10 arnperes per square decimeter. Excellent low stress deposits were obtained with `the stress being llower at 10 a./drn.2.

The features and principles underlying the invention described above in connection wtib speciic exempliiications will suggest to those skilled in the art many other modifications thereof. lt is accordingly desired .that tbe appended claims shall not be limited to any specific feature or details thereof.

We claim:

l. An aqueous acid gold plating bath containing about 10-200 g./l of a salt of a weak, stable organic acid,

4 to 16 g./l. of gold added as an alkali gold cyanide and, about 1/2 to about 20 g./l. of a compound having the formula N-X R wherein R is selected from tbe group consisting of hydrogen, an alkyl group of up to 6 carbon atoms, and an aryl group of up to 6 carbon atoms, and Where X is selected from the group consisting of /R1 u N C-NH2 and OH, Where R1 is selected from the group consisting of hydrogen, an alkyl group of up to 6 carbon atoms and an aryl group of up to 6 carbon atoms, said bath being adjusted to a pl-l of 2.5 to 7.0. 2. An aqueous, acid gold plating solution according to claim 1 wherein the organic acid ion is the anion of citric acid.

3. A process for electrodepositing gold which comprises electrolyzing a solution consisting of about 10 to 200 g./l of the salt of a weak, stable organic acid, about 4 to 16 g./l of gold added as an alkali gold cyanide and, about 1/2 to 20 g./l of a compound having the formula wherein R is selected from the group consisting of hydrogen, an alkyl group of up to 6 carbon atoms, and an aryl group of up to 6 carbon atoms, and Where X is selected from the group consisting of o-Ntn and OH, Where R1 is selected from the group consisting of hydrogen, an alkyl group of up to 6 carbon atoms and an aryl group of up to 6 carbon atoms,

said bath being adjusted to a pH of 2.5 to 7.0.

4. An aqueous acid gold plating bath containing about itl-20() g./l. of a salt of a Weak, stable organic acid,

4 to 16 g./l of gold added as an alkali gold cyanide and,

about 1/2 to about 20 g./l. of a hydrazine compound,

`said bath being adjusted to a pH of 2.5 to 7.0.

5. An aqueous acid gold plating bath containing about 10-200 g./l. of a salt of a weak, stable organic acid,

4 to 16 g./l. of gold added as an alkali gold cyanide and.

about 1/2 to about 20 g./l. of liydrazine,

said bath being adjusted to a pH of 2.5 to 7.0.

6. An aqueous acid gold plating bath containing about 10-200 g./l. of a salt of a Weak, stable organic acil,

4 to 16 `g./l. of gold added as an alkali gold cyanide and,

about 1/2 .to about 20 g./l. of a liydrazine salt,

said bath being adjusted to a pH of 2.5 to 7.0.

7. An aqueous acid gold plating bath containing about 10-209 g./l. of a salt of a Weak, stable organic acid,

4 to 16 g./l. of gold added as an alkali gold cyanide and,

about 1/2 to about 20 g./l. of alkyl bydrazine containing up to six carbons in the alkyl group,

said bath being adjusted to a pl: of 2.5 to 7.0.

8. An aqueous acid gold plating bath containing about 10-200 g./l. of a salt of a weak, stable organic acid,

4 to 16 g./l. of gold added as an alkali gold cyanide about 1/Iz to about 20 g./l. of phenyl hydrazinc,

said bath :being adjusted to a pH of 2.5 to 7.0.

9. An' aqueous bath as claimed in claim 1 wherein said bath contains in addition up to 18 g./l. of a base metal ion (calculated as metal). 

1. AN ANQUEAUS ACID GOLD PLATING BATH CONTAINING ABOUT 10-200 G./L OF A SALT OF A WEAK, STABLE ORGANIC ACID, 4 TO 16 G./L. OF GOLD ADDED AS AN ALKALI GOLD CYANIDE ABOUT 1/2 TO ABOUT 20 G/1 OF A COMPOUND HAVING THE FORMULA 